For most people running 45 miles would be the biggest challenge they are ever likely to undertake.
But Simon Douglass has been facing a far more formidable battle over the last year.
Because the 42-year-old was diagnosed with a brain tumor in February 2012 after suffering an epileptic fit.
Now he is preparing to take on a gruelling run from his Aspley Guise home to Addenbrookes Hospital in Cambridge, where his brain surgery took place.
He is hoping to raise money for the Seve Ballesteros Foundation and increase awareness of brain cancer.
Simon, known as Chippy, had an epileptic fit at his work in Peterborough and had to be rushed to hospital.
Doctors discovered he had a large brain tumor and after they initially told him it couldn’t be operated on, he was transferred to specialist Addenbrookes.
There he was told the tumor could be operated on, but that it couldn’t be completed removed.
Three agonising weeks later he underwent successful surgery – but the timebomb in his brain still exists.
“I thought only old people and young children got brain tumors. People are touched by breast cancer every day, but perhaps not brain tumors,” he said.
“Fortunately, it was a low grade tumor, not an aggressive tumor.
“They don’t know how long it will be there and how quickly it had grown.
“But the long term prognosis is that it will grow at some stage.
“When that is we don’t know. It could be next month or decades away.”
Simon, who is married with two young boys aged eight and six, has since returned to his job at Silver Spoon, although he spends four days a week working from home as the epileptic fit has ruled out driving.
“It gives me something to focus on, and working from home means I get to take my children to school and pick them up,” he said.
But the thing which has really focused his mind is running.
Already a member of Marshalls Athletics Club and with five marathons behind him, Simon added: “Running helped me to relax and made me feel better about myself.
“I also wanted to do something that ended at the hospital where I had my brain surgery.
“As it is marathon season there are lots of people asking for donations so I thought it had to be something above and beyond.”
He is now hoping to finish the run, which will take place on Saturday, May 4, in around nine hours.
“It isn’t a time thing, it is a completing it thing,” he added.
“When you do a marathon you are running with lots of other people. This is an unknown distance and I’ll be on my own.”
The Seve Ballesteros Foundation, part of Cancer Research UK, was founded after the death of the champion Spanish golfer who died of brain cancer is 2011.
“Part of Seve’s legacy was to set up this foundation,” Simon said.
“He was one of those flamboyant characters who lived life to the full and he wanted that to live on in his memory.”
Rally driver Richard Burns also died of the same kind of brain tumor Simon has.
“I have got to try and live with it,” he added.
“It is there in the background, but it can’t effect my daily life.
“My best advice to anyone else affected would be listen to the doctors. I had a number of people who went off looking at the internet and came back with so many myths and untruths.
“Speak to the experts. Everyone else is trying to be kind and do their bit, but they don’t know.
“And don’t expect all the answers straight away.”
People can sponsor Simon by visiting his Cancer Research fundraising page